3D coordinates not supported for bbox search parameter

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STAC item-search API explicitly allows 3D coordinates for bbox search parameter:

bbox Represented using either 2D or 3D geometries. The length of the array must be 2*n where n is the number of dimensions

This is implemented in pgstac backend:

async def test_bbox_3d(load_test_data, app_client, load_test_collection):
    # ...
    australia_bbox = [106.343365, -47.199523, 0.1, 168.218365, -19.437288, 0.1]
    params = {
        "bbox": australia_bbox,
        "collections": [coll["id"]],
    }
    resp = await app_client.post("/search", json=params)
    assert resp.status_code == 200

But not in stac-fastapi where only 2D coordinates are enforced in str2bbox method:

def str2bbox(x: str) -> Optional[BBox]:
    """Convert string to BBox based on , delimiter."""
    if x:
        t = tuple(float(v) for v in str2list(x))
        assert len(t) == 4, f"BBox '{x}' must have 4 values."
        return t

    return None